The light novel Oreimo extra story (Oreimo after) is the one that takes place during the time of Ero manga sensei vol 3:
this is that part:
''Suddenly, turned to a boy walking ahead.
I wonder why, huh? It's not like he had any unique features like the 3 walking with me.
The boy who looked like he was either a 3rd grade junior high, or 1st grade high school student, was carrying with great care a tablet computer with both hands, while muttering something alone.
Looking from the sidelines, it could also look like he was ----talking to the computer.
I wonder if he's connected to 'someone', or something?
His face had a tint of blue, he was very nervous, and he was walking heavily to what appeared to be the bookstore.
That kind of sight was something I knew all too well.
It was on that unforgettable summer day.
The day I came to this city for the first time. ''